Mighty, Mighty Head

My favorite saison yeast is Wyeast 3711, French Saison. I have talked about it before: it has a nice spicy flavor and attenuates without much fuss. My standing joke is that this yeast will ferment your concrete floor if you let it sit. The thing is, the saisons I bottle almost always end up a bit over carbonated. I do not know if this is just the 3711 continuing to work, or if I am picking up a slight infection. The bottles do not gush, but you can only pour about half of the beer before you run out of space. The flavor is still OK, so if it is infected it is a pretty benign critter. But when those beers are poured man do they end up with one whipped cream like head. I am surprised the head is so big and long lasting, as I thought the continuing fermentation would tend to break down components in the beer which contribute to head formation.